As a cooling device (heat sink) that cools a heat-generating body, such as an insulated gate bipolar transistor (IGBT) component of an inverter for an electric vehicle or the like, a cooling device in which plural fins are provided in a box-shaped case and fluid channels are formed in the case is known (for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-296748). In the cooling device disclosed in JP-A No. 2004-296748, the fins forming the fluid channels are provided protruding from an inner face of a top wall of the case. An IGBT component or the like is attached to the outer face of the top wall, and the cooling device is structured such that heat generated by the IGBT component or the like is transferred through the top wall of the case to the fins The fins are cooled (heat is exchanged) by a cooling medium such as water or the like flowing through the fluid channels.
When the cooling medium flows through the fluid channels, internal pressure in the case rises. Accordingly, the top wall of the case is commonly assured of a predetermined stiffness, by a plate thickness thereof being increased. However, when the plate thickness of the top wall of the case is made thicker, a heat transfer rate at which the heat from the IGBT component or the like is transferred to the fins falls. As a result, cooling efficiency of the IGBT component or the like falls.